1. Field of the Invention
The present invention generally relates to a polishing pad, a polishing system, and a polishing method, in particular, to a polishing pad, a polishing system, and a polishing method capable of achieving a better polishing uniformity for the surface of a workpiece.
2. Description of Related Art
With progress of industrial technology, planarization processes are usually adopted for producing various devices, and a polishing process is one of the planarization processes often employed in the industry. Generally, in the polishing process, a fixed workpiece is pressed on a polishing pad by a pressure applied to the workpiece, and capable of moving relative to the surface of the polishing pad. As such, the surface of the workpiece is partially removed through friction generated by the above relative movement, and thus gradually becomes planarized.
FIG. 1 is a schematic top view of a conventional circular polishing pad. The circular polishing pad 110 includes a plurality of concentric circular grooves 120. The concentric circular grooves 120 are used to accommodate or remove residues or by-products generated by polishing, and enable a workpiece 130 to be easily detached away from the circular polishing pad 110 when the polishing process is completed.
During the polishing process, the circular polishing pad 110 rotates, and the workpiece 130 in contact with the surface of the circular polishing pad 110 rotates as well, expecting that every portion on the surface of the workpiece 130 may contact the concentric circular grooves 120. However, each of the concentric circular grooves 120 on the conventional circular polishing pad 110 has a circular shape, and the workpiece 130 rotates around its central axis. Thus, when a particular point moves periodically to a position where a direction between the particular point and the center of the workpiece 130 is perpendicular to a tangential direction of the grooves, the particular point will be constantly at a groove position or a non-groove position. For example, if the particular point is at the groove position, points adjacent to the particular point would be constantly at the non-groove positions, thus affecting the polishing uniformity. Moreover, the above problem gets worse at positions closer to the central portion of the workpiece 130, as the central portion of the workpiece 130 is almost constantly in contact with a specific position (for example, the groove position or the non-groove position) on the circular polishing pad 110 during the whole polishing process. Therefore, the polishing rate of the central portion of the workpiece 130 is lower or higher than the polishing rates of the other near portions, depending on whether the central portion is constantly in contact with the groove position or the non-groove position. The problem of non-uniform polishing rate of the workpiece 130 may eventually degrade the reliability of the device.
Therefore, a polishing pad and a polishing method are required to provide a better polishing uniformity.